The only way I can tell is they go on hard, or they don't spin on without any effort. I've only replace a handful of props, and this was always the case. There wasn't anything you could see, but when they started going on like the threads were beginning to get worn, I replaced em. Some on here say props are cheap, so replace em. Some others say if you cant see anything wrong, don't waste a prop, use em. I go with the guys that say replace, mainly because I don't want it falling out of the air due to a prop coming off. There is school of thought that claims props can be spun off because of breaking, slowing down abruptly. The motors don't change direction when doing this breaking, so I believe this to be bs. Hard to screw on, or off, they probably need to be changed.

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Before each flight, check your props (especially around the hub area) for hairline cracks, stripped hub threads, or any other sign of damaged plastic. If you see anything odd, play it safe and change the prop.

Wednesday evening my front left prob (black) come of at 217 feet just almost 2 minutes into my flight. I just started a long curved turn towards my friends house up the road when it fell. I've searched for the prop with out any luck,really wanted to see the threads to try to find out if it was a mistake on my part or part failure. Last night after going to two different stores each only having one pair, I set down to try to compare new threads to old then grabbed my P3s to check my threads and the light hit it just right I noticed small trace of plastic all the way down the threaded shaft. To me that says it stripped off in flight. Haven't flown it since except for when I retrieved it to see if it would still fly wanted to today but 30+mph wind gust all day. Waiting for calmer wind for a true test flight.

Wednesday evening my front left prob (black) come of at 217 feet just almost 2 minutes into my flight. I just started a long curved turn towards my friends house up the road when it fell. I've searched for the prop with out any luck,really wanted to see the threads to try to find out if it was a mistake on my part or part failure. Last night after going to two different stores each only having one pair, I set down to try to compare new threads to old then grabbed my P3s to check my threads and the light hit it just right I noticed small trace of plastic all the way down the threaded shaft. To me that says it stripped off in flight. Haven't flown it since except for when I retrieved it to see if it would still fly wanted to today but 30+mph wind gust all day. Waiting for calmer wind for a true test flight.

Yes I will definitely keep a better eye on them even though I'm not ruling out pilot error in preflight. I was in a hurry to get it in the air due to daylight fading fast, I was multitasking my setting up. Won't make that mistake again. I lucked out with just a crack on my top shell in the middle side and a bent yaw arm really lucked out with yaw arm because I managed to strengthen it up with out the cast aluminum snapping. As soon as I save me up enough pennies its new shell and yaw arm!

If a prop did so much as hit an object, the force could be enough to strip the thread. And since it is often turning at high speed, it usually hits the object multiple times... like an impact tool. And we know how impact tools can remove a stubborn nut or bolt.

So if your props have damage marks on the leading edges, there's a possibility that the threads have seen better days. Replace them.

Trust me from now on I wil replace them as soon as they hit something and will not rush when getting ready to fly. I had a small window to fly I put a pair of props on spun them down while getting remote out put last pair on spun them powered up tablet and put it on the remote mount. Next grabbed P3s powered it up set it down with out checking them and started linking everything a minute 30 something seconds later video shows landing up then sky landing gear video gone. Lesson learned though and props being $12 and now knowing I have 3 local stores that carry them and not wait on them to ship no reason not to plus cheaper then a $60 shell and $20 yah arm. I was Lucky it dropped where it did in tall grass that the wind blew over so it had a thick cushion and not like some of the stories I've been reading on here.

I have never taken my props off since the day I originally put them on. Each flight I give them a little twist to make sure they are tight and when I say twist I just put enough pressure on them to make sure they aren't loose. My thoughts have been that repeated off and on could lead to problems. Does anyone know if the people that are losing props mid flight have been putting them on and off each time or just leaving them on. If I need to travel in the car with my drone I just place it in the cardboard case that came in the box with the props still on.

I used to put them on and twist enough to snug them up. They were still comfortably snug but removed easily enough after flight.

Then, I specifically looked for and bought a case that I could put my aircraft in while leaving the props on. I firmly believe that the double motor rev after start up is specifically meant to tighten the props, which is why they are called self tightening propellers.

What I've noticed since I've been leaving the props on is that when I do try to take them off after a period of time and several flights, they are VERY snug, significantly tighter than when I put them on in the first place, to the point of needing the motor clamp to take them off.

That not only confirms for me that they ARE self tightening, but also that I am more comfortable NOT taking them off any more than necessary.

I know that's not too helpful to anyone thy already has a case they are happy with, but it's an observation that may be worthwhile.

And for me, always OEM props and batteries.

Oh... and one other unintentional test... sudden power loss will fire the two counter rotating props off like rockets. That MAY help explain SOME circumstances.

Source: my AC was hovering. I had the landing gear firmly in one hand. Due to a longer story, I had no choice at the time but to pull the battery out. Those two props shot skyward until gravity brought them back.

I'm trying to imagine why the counter rotating props would be more inclined to spin off than the others ...

The motors turn in the required direction for the props, 2 x CW and 2 x CCW ... so in theory there should be no difference. If props were to come off because of instant stop of motors - then all 4 should do it or any that are not 'snugged up'.

My props are still the first ones I ever fitted ... the spare ones never been out of the bag. I remove props for putting model in its bag. Spin them on and then the small amount extra to 'snug them up' by hand.
Never needed the prop removal tool ... props always similar 'snugged up' after multiple flights ...

I'm trying to imagine why the counter rotating props would be more inclined to spin off than the others ...

Cheers
Nigel

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I agree, I haven't figured out why it happens but I didn't spend much time at it either. If the motors counter rotate and the threads are reverse threaded it doesn't make sense to me either but if anyone else wants to try it (Nigel you're always good for a test or two ) they're welcome to it!

There are enough warnings NOT to take your battery out while in flight that I don't plan to do it again any time soon...

To be honest ... I don't see taking battery out as a reason for props to fly off ...

But when you let go sticks when at full forward flight - then props are stressed ...

Why the difference ?

If you remove the battery - then there is no power there and all is dead. The motors will freewheel without any braking effect at all.

But with battery in place - you could in theory have braking because a BL motor acts like a generator when freewheeling and shorting or applying reduced power causes motor to slow - as you see model abruptly stop in the air when you let go sticks, compare when you shut down motors by left stick while still power available to when you spin props by hand when not powered ... by hand they rotate more revolutions etc.

My personal view is that props flying off is either because of damaged fixings or operator error by not snugging up before flight.
The rotation of the props / motor combo is such that they should tighten as you increase throttle to take-off ..

I have never taken my props off since the day I originally put them on. Each flight I give them a little twist to make sure they are tight and when I say twist I just put enough pressure on them to make sure they aren't loose. My thoughts have been that repeated off and on could lead to problems. Does anyone know if the people that are losing props mid flight have been putting them on and off each time or just leaving them on. If I need to travel in the car with my drone I just place it in the cardboard case that came in the box with the props still on.

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Mine come off almost after every flight session unless it's the weekend because I take mine to work all most every day, I work out doors as a foreman building metal buildings. So my work takes me to some ideal areas to fly being wide open and like taking pics of some of my work and I keep it in a hard shell backpack case due to it needs a rugged case to survive my work truck. I'm leaning to the theory that props coming off is due more to prop stricks because it wasn't to long after flying in strong winds it tipped over on the landing, few days later my bird falls out of the sky. Also come to that conclusion after a lot of reading on here but still a possibility I just didn't have it on good or right as I was rushing to fly due to the setting sun and the flying pestty bugs that come with it

To be honest ... I don't see taking battery out as a reason for props to fly off ...

But when you let go sticks when at full forward flight - then props are stressed ...

Why the difference ?

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To be honest, I have no clue. What I can be absolutely certain of is that the props were put on correctly, and snugged individually as I always do.

What also know for certain is that the split second the battery was removed, two of the same colour propeller, though I can't remember if they were the black or the silver, shot off like a rockets. Instantly.

To be honest, I have no clue. What I can be absolutely certain of is that the props were put on correctly, and snugged individually as I always do.

What also know for certain is that the split second the battery was removed, two of the same colour propeller, though I can't remember if they were the black or the silver, shot off like a rockets. Instantly.

What I don't know is if the two actions are related.

You're making me want to try it again!

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I could see if they were lightly spun on like if been doing and the motors stopped abruptly like battery removed or if mine had some hiccup the momentum of the props to keep spinning after the sudden stop of the shaft. After all the reading I've done on here I snug them down around an 1/8+ of a turn, being a gear head spinning enough wrenches and snapping bolts I kinda go by fill. I agree now with what I read in one reply prop strick replace, not saying you hit anything but I did have a prier rough landing do to wind that made it tip over when the landing gear touched down.so my new rule of thumb is props hit anything replace and give them a good snug turn after you spin them down

Well, it was pretty new at the time, didn't have much of a clue what I was doing, and can't swear they were tightened because I was in the living room and it was maybe it's second time out of the box...

But it was kinda cool to see them go and because it was two of the same colour and it was so instant after the battery removal I figured the two were related...

But anything is possible... I'm not documenting it as a tested hypothesis!

Well, it was pretty new at the time, didn't have much of a clue what I was doing, and can't swear they were tightened because I was in the living room and it was maybe it's second time out of the box...

But it was kinda cool to see them go and because it was two of the same colour and it was so instant after the battery removal I figured the two were related...

But anything is possible... I'm not documenting it as a tested hypothesis!

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I've only had mine a little over a month so I'm far from an expert just been doing a lot of reading on here and coming to my own logical conclusion from my mechanical understanding, just the way my brain works lol

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